The present invention relates generally to systems for processing signals, and more particularly to systems for processing the phase of signals.
Missile guidance systems are known which rely on target-generated radiation for radio frequency homing. The angle needed for guidance is determined from the difference in phase between radiation wavefronts arriving simultaneously at two antennas which are equally spaced apart about the missile's center-line and rolling with the missile. Since the antennas look at all planes of incoming radiation during each roll cycle, the phase difference between received wavefronts will be a sinusoidal function of time at the constant roll frequency. In the circuitry following the antennas, the two antenna outputs are first processed to provide two video signals which are proportional to the sine and cosine of the phase difference between received wavefronts, respectively. Next, the two video signals are multiplied by two quadrature signals at 12 KHz and summed to produce a 12 KHz carrier that is phase-modulated by a modulating wave whose amplitude equals the phase difference between received wavefronts. In the past, the modulating wave was recovered by supplying the phase-modulated wave to a phase-locked loop, detecting the resulting frequency modulation as the control voltage of the voltage-controlled oscillator in the loop, and thereafter passing the output through an integrator to detect the phase-modulation. Since the control voltage is a small quantity, the output of the integrator had to be amplified by a factor of 100.